Access body of Message actuactor through logic bricks
No, there is no way.

The reason is simple: what should happen when there are two or more messages?

There are way too much options to process a body (and several bodies). The information you could get is if an message with a certain content was received. The filter by subject already does that.

I agree the API looks inconsistent, as you can set a body without any use (without using Python). I see it as simplification, when you have a lot of simple message senders, but just a few  (more complex) listeners. I usually use the body when I have more information than the pure existence of a message (subject) can express.